The present invention relates to semiconductor devices and more particularly to power semiconductor modules which combine a plurality of semiconductor chips in which power transistors such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs are formed.
A power semiconductor module which combines several power semiconductor chips such as transistors and diodes typically includes a metal base plate for diffusing heat generated by semiconductor elements, a wiring layer having a wiring pattern for mounting semiconductor chips, and an insulating substrate for insulation between the wiring layer and the metal base plate.
In recent years, efforts toward more compact power semiconductor modules have been pursued in order to decrease the packaging area and reduce the cost of parts. For example, Japanese Unexamined Patent Publication No. 2008-166461 discloses a bidirectional switch module in which two transistor chips and two diode chips, making up a bidirectional switch, are sealed in a single semiconductor package.
Japanese Unexamined Patent Publication No. 2005-243685 discloses a technique for coupling an electrode pad and a lead in a power transistor chip by a thick coupling plate in order to improve the heat radiation efficiency of a semiconductor package with a resin-sealed power transistor chip and reduce the on-resistance of the transistor. The coupling plate disclosed in this document is a metal plate with a flat upper surface which has a thin portion and a thick portion, in which the lower side of the thick portion is coupled to a source electrode pad through a conductive adhesive and the lower side of the thin portion is adhered to a source lead through a conductive adhesive.
Japanese Unexamined Patent Publication No. 2005-026294 discloses a technique which ensures stable bondability of a semiconductor package with a resin-sealed power transistor chip by arranging a source electrode pad and a gate electrode pad over the power transistor chip surface so as to prevent contact of a wire bonding tool with lead posts.